One type of glass filament forming process uses an electrically heated stream feeder that is fed glass marbles. The heated feeder melts these marbles into a body of molten glass primarily by conduction and radiation and discharges the molten glass as streams. Mechanical or fluid means can be used to attenuate the streams into glass filaments.
Competition in glass filament products demands a great deal from marble melting stream feeders. Economic conditions call for marble melting stream feeders that provide increased molten glass throughput to increase glass filament production. And a more demanding community of glass filament product users calls for uniform filament size in products.
But the goals of both increased production rates and uniform filament size from marble melt stream feeders conflict with each other. Of course, more feeders will increase glass filament production. But these feeders are normally made from expensive platinum alloys. Therefore greater melting capacity for conventional small stream feeders presents a more attractive choice.
Melting glass marbles by a stream feeder is a complex and sensitive operation that directly affects the quality of glass filaments produced, especially at higher production rates. For example, introduction of glass marbles to a feeder has a chilling effect that disturbs the temperature pattern of molten glass in the feeder. This disturbance causes viscosity variations in the molten glass streams discharged from the feeder. These viscosity differences produce glass filaments having undesirable nonuniform diameter variations along their lengths. And these nonuniformities tend to become even more pronounced with attempts at higher production rates.